An example of conventional surface mount type chip antenna using a conductive wire is shown in FIG. 20 (see the Japanese Patent Laid-Open No. H11(1999)-205025). This drawing shows a perspective view of a chip antenna 90, which is provided with a conductive wire 92 spirally wound inside a base 91 in its lengthwise direction, a power feed terminal 93 which is formed over the surface of the base 91 and to which one end of the conductive wire 92 is connected, and a grounding terminal or terminals 94 formed at least either within or over the surface of the base 91. Reference sign 95 denotes an open end, and 96, a ground pattern. As this chip antenna 90 has its conductive wire 92 formed inside the base 91, its manufacturing process is complex. Because of this formation of the conductive wire 92 inside the base 91, it is also impossible, after the manufacture, to vary the length of the conductive wire to adjust the resonance frequency or to match the input impedance to, for instance, 50 ohms. Furthermore, even if the conductive wire is spirally wound around the other surface of the base, when this chip antenna is to be mounted on a substrate, the presence of the conductive wire outside would make it correspondingly difficult to settle it on the substrate, which means a problem in mounting stability. Even after its mounting, if a bending force works on the substrate, a stress will arise in the chip antenna terminal portion and, moreover, the antenna will be affected by a distortion due to the difference in thermal expansion coefficient from the substrate.
One of the attempts to eliminate this manufacturing complexity and the poor mounting stability is, for example, a chip antenna disclosed in the Japanese Patent Laid-Open No. 2002-16419. In this surface mount type chip antenna, a level-gapped portion 120 is provided around the full circumference of a base 110 as shown in FIG. 21, a spiral conductive wire 130 is wound around this level-gapped portion 120, and the two ends of this conductive wire 130 are connected via conductive caps 140 and 150, each covering the whole circumferential face of terminal portions at both ends of the base 110.
These surface mount type antennas find a wide variety of applications including not only main antennas for cellular phones and the like but also chip antennas for wireless LANs and the Global Positioning System (GPS), and each has to be mounted in a narrowly limited space in the cellular phone or the like. As the frequency band of the electric wave used in telephone communication via the surface mount type antenna (800 to 900 MHz) and that of the GPS electric wave (1700 to 1900 MHz) differ from each other, both the antenna for telephone communication and that for-receiving GPS information have to be accommodated in the already tight space.
In addition, the substrate over which the surface mount type antenna is arranged is often mounted with devices emitting an electromagnetic wave, such as a loudspeaker, a vibrator and more recently a small CCD camera, accommodated in a metallic case. The limitation of the space frequently obliges the antenna to be arranged close to the loudspeaker and/or the vibrator, and this arrangement might invite mutual interference between the metallic functional components, such as the loudspeaker, vibrator and small CCD camera, and the antenna.
A communication device such as a cellular phone is always required to be not only small and suppressed in height but also adaptable to a wide bandwidth and highly efficient. The surface mount type chip antenna illustrated in FIG. 21, though improved in mounting ease, embodies no consideration for the performance requirements of the antenna, such as a broad bandwidth and a high radiation gain. For instance, as shown in FIG. 21, the level-gapped portion 120 is disposed around the whole circumferential face of a prismatic base, and the terminal portions 140 and 150 are also provided all around the circumferential face. While these arrangements are intended to eliminate the directionality of the power feed electrode and increase the ease of mounting, they also involve a problem that the terminal portions thicker than the level-gapped portion, which constitutes a greater part of the side faces of the base, limit the thickness of the base. In order to obtain an antenna having a broad bandwidth and a high radiation gain, it is necessary to reduce the Q-value, which is in reverse proportion to these characteristics. To be more specific, this is achieved by using a material of a low relative dielectric constant or increasing the thickness of the base. On the other hand, the higher the relative dielectric constant of the base, the shorter the radiation electrode. On account of these factors, if the bandwidth and the radiation gain are to be increased while keeping the relative dielectric constant of the base unchanged, the thickness of the base will have to be increased. Therefore, in the case illustrated in FIG. 21, even if required characteristics are satisfied, the additional arrangement of the level-gapped portion over it will entail a problem that the base is further thickened. Moreover, as the sectional area of the base is reduced correspondingly to the presence of the level-gapped portion, it is necessary to increase the length of the base in order to secure a sufficient winding length of the conductive wire. Furthermore, in the manufacturing aspect too, the conventional configurations require a groove to guide the conductive wire or terminal caps, which adds to the manufacturing complexity and cost.
Also, because of the aforementioned requirement for reductions in size and height, the chip antenna and metallic functional components, such as a loudspeaker and a vibrator, are often arranged close to each other over the circuit substrate. In such a case, it is desirable to prevent mutual interference.